Mercury , thermal expansion coefficients

We found the latter factor-voids to be important. Experimental results showed that when green coke was calcined under the new methods, and the derived calcined coke was observed by scanning electron microscopy (Figure 2) and its pore size distribution was measured by mercury porosimetry (Figure 3), microcracks of significant sizes (1 to 60 microns) were developed. This was an important contribution to the reduction of the thermal expansion coefficients of the calcined coke processed under the new method. 

The low melting point (234 K) of Hg results in its being a unique metal. Its high thermal expansion coefficient makes it a suitable liquid for use in thermometers, and it has widespread application in barometers, diffusion pumps and in Hg switches in electrical apparatus. An older use was in mirrors. Some other metals dissolve in mercury to give amalgams, their uses are varied, for example ... 

The final table gives the cubic thermal expansion coefficient a, the isothermal compressibility coefficient and the speed of sound u for liquid mercury as a function of temperature. These properties are defined as follows ... 

Table tr.1-175 Linear thermal expansion coefficient a of mercury compounds ... 

In this work the merits of the use of a natural fibrous mineral, sepiolite, as a binder to produce titania based monoliths of high mechanical strength and abrasion resistance is discussed. The monoliths of square channels were conformed with an initial 7.5 channels cm and 1 mm wall thickness. TTie textural characterization was made by mercury intrusion porosimetry (MIP), nitrogen adsorption/desorption (BET), and X-ray diffraction (XRD). The mechanical resistance, dimensional changes and weight losses al each stage of heat treatment were also determined. The thermal expansion coefficients (TEC) of the monoliths were determined between 200 and 400 C, since in practice the usual working temperature of DENOX catalysts lies between 250°-350 C. 

The equation-of-state data for mercury are accurate enough to permit determination of derivative quantities such as the isothermal compressibility Xt snd the thermal expansion coefficient Up. These may be obtained at various constant temperatures as functions of density or pressure. Experimental results for t are plotted against density in Fig. 4.11 the thermal expansion coefficient exhibits similar behavior (Gotzlaff, 1988). The most interesting feature of Fig. 4.11 with regard to the MNM transition is the sharp increase in xt observed in the range between 4 and 8 g cm for temperatures not far from T. This effect is related to development of critical density fluctuations and its appearance clearly demonstrates the importance of such fluctuations in this density range. We return to the interplay between the critical density fluctuations and the MNM transition in Sec. 4.6.2. 

Certain alloys of iron, nickel, and cobalt (Kovar, Fernico, etc.) have thermal expansion curves which nearly match those of borosilicate glasses, and a good bond may be formed between the two. Kovar is similar to carbon steel in its chemical properties. For example, it oxidizes when heated in air and is not wet by mercury. It may be machined, welded, copper brazed, and soft soldered. Silver solders should not be used with Kovar since they may cause embrittlement. At low temperatures Kovar undergoes a phase transformation, and the change in expansion coefficient below this temperature may be sufficient to cause failure of a glass-to-Kovar seal. The transformation temperature usually is below... 

A problem which arises when a read-out chip of for example silicon is attached to a detector chip of mercury cadmium telluride is the mechanical damage which may occur when the array is cooled to cryogenic temperatures for operation. The stress is due to a mismatch in the coefficients of thermal expansion between the two materials. 

Liquid in Glass Thermometers. Mercury-in-glass thermometers (or better yet, mercury-in quartz) function well between -25°C and 360°C their typical precision is 0.1 K. They must be corrected for (1) relatively small pressure effects and (2) a relatively large "exposed-stem correction," due to the different coefficients of thermal expansion of mercury and glass in the part of the thermometer not immersed in the system being measured. 

Bimetallic Thermometers. These use two metals of different coefficients of thermal expansion that are bonded together their heating bends the device, and an electrical contact can then be made or broken. Thermometer coils that expand/contract with temperature and make or break contact with a mercury electrode are used in household thermostats and industrial control apparatus. 

As stated earlier, temperature and pressure do not have large influences on the densities of solids and liquids. Nevertheless, the fact that mercury in a thermometer rises or falls with changing temperature shows that the effect of temperature on liquid density is measurable. Coefficients of linear and cubic (volume) thermal expansion of selected liquids and soiids are given as empirical polynomial functions of temperature on pp. 2-128 to 2-131 of Perry s Chemical Engineers Handbook. For example, the Handbook gives the dependence of the volume of mercury on temperature as... 

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